Dialkyl thionocarbamate method

ABSTRACT

High-purity dialkyl thionocarbamates are economically produced by reacting suitable xanthates with alkyl amines in the presence of a dissolved catalyst. Nickel and palladium salts are preferred catalysts. Thionocarbamates produced by the method of the invention are a desirable flotation reagent for certain refractory copper sulfide ores.

United States Patent [191 Bolth et al.

[ Sept. 23, 1975 DIALKYL THIONOCARBAMATE METHOD [75] Inventors: FranklinAnderson Bolth, Baltimore,

Md.; Ronald David Crozier, Bedford, N.Y.; Lawrence Evans Strow,Baltimore, Md.

[73] Assignee: Minerec Corporation, New York,

22 Filed: July 13, 1973 21 Appl. No.: 379,114

[52] US. Cl 260/455 A; 252/61; 209/166 [5 1] Int. Cl. C07C 155/02 [58]Field of Search 260/455 A [56] References Cited UNITED STATES PATENTS2.69l,635 l0/l954 Harris et al. 260/455 A 2.723.989 ll/l955 Harman260/455 A OTHER PUBLICATIONS Biigemann et al., Schwefel, Selen-,Tellur-Verbindungen, 1955, p. 832.

Primary Examiner-Elbert L. Roberts Assistant Examiner-D. R. PhillipsAttorney, Agent, or Firm1ames J. Burke, ll

[ ABSTRACT 13 Claims, No Drawings D] ALKYL THIONOCARBA M ATE \IE'II-IOI) BACKGROUND OF- THE INVENTION l. Field of the Invention Thepresent invention relates generally to the production of dialkylthionocarbamates. also sometimes referred to as thiourethanes. Compoundsof this type are defined by the general formula where R and R are alkylradicals. These products are known to be useful as flotation reagents inthe recovery of minerals from ores and concentrates.

In its more specific aspects. the present invention relates to theproduction of high purity dialkyl thionocarbamates from an alkali metalxanthate and an amine in a onestage. catalyzed reaction. It has beendetermined. for example. that isopropyl ethyl thionocarbamate made bythe process of the present invention is a superior flotation reagent forcertain ores. when compared to a commercial grade of the same reagent.

2. Prior Art The production of dialkyl thionocarbamates. and their useas flotation reagents. is well known in the art. In essence. an alkalimetal xanthate is first reacted with an alkyl halide to form a dialkylxanthate. This is then reacted with an aliphatic amine to produce thedesired compound and a mercaptan. The latter can be distilled off. andthe organic and aqueous phases separated. In practice. however. problemsarise.

In the initial formation of the alkali metal xanthate by reaction of analkali metal hydroxide with carbon disulfide and an aliphatic alcohol.temperatures must be closely controlled to avoid significanttrithiocarhonate formation. Close temperature control is also necessaryin the intermediate reaction with an alkyl halide. The amine is thenintroduced and. after reaction. the organic reaction product isrecovered. However. this is said to contain only 50-90% of the desiredester. the remainder being mainly alkyl dithiocarbamate. dialkylxanthate and dialkyl trithiocarbonate.

In the prior art. the selection of reaction conditions always involved atrade-off between obtaining a reasonable reaction rate and yield ofdesired product. High temperatures improved reaction rate but alsoencouraged side reactions and decomposition of xanthate. The same istrue of long reaction times. In one regard. the present invention issurprising in using both higher temperatures and longer times than wouldbe taught by the conventional wisdom. while still producing a highpurity product.

Prior workers have argued that such an impure ester is advantageous. inthat costly and time consuming purification steps are avoided. It issaid that no benefit is gained by isolating and purifying theintermediates. so that a pure ester could be obtained. Such purificationsteps would indeed be costly. but in accordance with the presentinvention. a high purity product is obtained and the only purificationneeded is washing with \Vtlltll'.

OBJECT OF THE INVENTION It is a general object ol the present inventionto pro- \ltlt. an improved process lor producing dialkyl lllltltltCtlfll1tllltllL\ A further object ol'thc present invention is to providea process for producing dialkyl thionocarbantatcs ol high purity.

Another object of the present invention is to provide a process forproducing high purity dialkyl thionocarbamates wherein contamination byintermediate reaction products is avoided.

A still further object of the present invention is to provide improveddialkyl thionocarbamatcs which are useful as flotation reagents for oresand concentrates.

Various other objects and advantages of the invention will become clearfrom the following description of embodiments thereof. and the novelfeatures will be particularly pointed out in connection with the anpended claims.

DESCRIPTION OF EMBODIMENTS In essence. the present invention is based onour discovery that compounds of the type described can be produced withgood yield and in high purity form by directly reacting the xanthate andan alkyl amine in the presence ofa catalyst. The preliminary reactionwith an alkyl halide is thus eliminated. As catalysts. nickel salts areoperable but palladium salts are preferred. As set forth more fullyhereinbelow. differing reaction conditions are required for each salt.In the course of the process the catalyst material may be recovered forre cycling; this is economically essential. however. only in the case ofthe palladium salt.

In carrying out the invention. a technical grade of xanthate is preparedby conventional means. For example. sodium hydroxide. carbon disulfideand isopropyl alcohol are reacted under appropriate conditions to forman aqueous solution of sodium isopropyl xanthate. The technical grade isactually preferred to a laboratory or reagent grade. because itgenerally contains excess dissolved carbon disulfide. which is believedto assist later reactions in going to completion. possibly by the law ofmass action. However. more than 2% free alkali in the solution isdeleterious to the reaction. and should be neutralized.

The catalyst and amine are then added to the xanthate solution. Thecatalyst is added in the form of a soluble salt. such as nickel sulfate.palladium chloride. palladiumamine complexes or the like. Experienceindicates that less than all of the palladium salt goes into solution.but this is not a problem. The quantity of catalyst added is not deemedcritical. but is generally in the range of 0.002 to 0.02 mols palladium.calculated on a formula basis. per mol of xanthate. For nickel. thepreferred range is 0.0l to 0.02 mols per mol of xanthate. Additions athigher levels are neither deleterious nor beneficial.

An aqueous amine is added in stoichiometric excess not exceeding about200% of the mols of xanthatc; generally an excess of about l20'/r issatisfactory. Expressed differcntly. this is an excess of 20l00 r. Forpractical reasons the amine is limited to a chain of 14 carbon atoms.

When the palladium catalyst is used. the reaction is carried out at atemperature in the range of 50 to 90C. for periods ranging from /2 hourto l8 hours. Prc' l'crrcd conditions are C for lb hours in one instance.Lintlcr these conditions. it has been determined that palladium willcatalyze reactions producing a wide varict) ol' dialkylLlithionocarbamatcs.

Of course. the sodium hydrosulfide byproduct is quite distinct from themcrcaptan products produced by con ventional procedures; it isconsidered that the presence ofthe catalyst ions and dissolved CSprovides an environment wherein the hydrosulfide is formed to theexclusion of the type of byproducts which have plagued prior workers.noted hereinabove. However. the precise reaction mechanism is not known.and is undoubtedly complex.

The aqueous phase. which is dark with sodium hydrosulfide and containsthe excess amine. is separated from the organic phase by settling anddecantation or any convenient technique. The aqueous phase will containmost ofthe catalyst, in sulfide form. and should not be discarded ifrecovery is contemplated.

The product oil is washed with water several times to remove isopropylalcohol.

The resulting oil is dried by any convenient technique and is found tocontain from 98 to l7r of the desired ester. in the case describedisopropyl ethyl dithionocarbamate. Further. the only detectab e impurityis isopropyl alcohol. and not the various in. .rmediate reactionproducts of the prior art.

While nickel salts are operable as atalysts in the process for producingthe isopropyl esters as described hereinabove. it has been found thatyields are substantially greater when the palladium salts are employed.The reason for this is not known.

Understanding of the invention will be facilitated by reference to thefollowing specific examples thereof. which are to be construed asillustrative only and not in a limiting sense.

EXAMPLE I A technical xanthate solution (I500 ml.) containing 490.4grams of sodium isopropyl xanthate was treated with l6.3 grams NiSO 6H Oin water and 2437 grams ofa 694% ethyl amine solution at 80c. for 6hours. At the end of this time 37 l .5 grams of crude product wasseparated containing 3 l 3.7 grams of pure isopropyl ethylthionocarbamate.

EXAMPLE ll Dissolved salts of nickel and of palladium are both usefulcatalysts in the preparation of isopropyl ethyl thionocarbamate. In thefollowing table a technical xanthate solution containing 44.3 grams ofsodium isopropyl xanthate was treated with 2L6 grams of 70% ethyl aminesolution and the listed catalyst for 6 or more hours at 80C.

The results were:

(A TALYSI (IR. ('Rllll' YlFll) (1R llIRl: YIFLD none 3.3 3.27 l.47 gr.NiSO .hH. 29.0 2X60 10 gr. PdCL, 3h." 35.28

Similar results may be had with the chlorides and nitrate salts ofnickel.

EXAMPLE lll Palladium chloride is useful as a catalyst in the productionof all dialkyl thionocarbamates. The following table records data from aseries of such preparations in which several technical xanthatesolutions were reacted with 40% methyl amine solution (B) and ethylamine (A) in the presence of palladium chloride and also with nocatalyst at all present. The reactions run with isopropyl xanthate wererun l6 or more hours at C. Those reactions that utilized the otherxanthates listed were run 2 or more hours at 70C.

Grams of Xanthatc Xanthate Catalyst Amine Yield Purity Used Used UsedUsed Pct. Pct.

isopropyl 443g. None =Zh.lg. 29.09 90.42 lsupropyl 44.3g. PdCl.. .-lg.B=26.lg. 878R 95.00 n-Butyl 481g. None =26. lg. 53.5 65.0 n-Butyl 482g.PdCM-lg. ll=2h.lg. 84.9 85.4 n-Butyl 48.23.. None A=Z l .6g. I81 95.0n-Butyl 482g. Pd(l.. .-lg. A=2l.6g. 732 K43 lso-Butyl 482g. None B=26.lg. 60.9 92.7 lso-Butyl 482g. PdCl.,-lg. B=2(1.lg. 85.5 9| .5 lso-Butyl482g. None =2 l .(ig. ltytl 99.0 Iso-Butyl 482g. PdCL. I g. =2 l .(ag.68.9 96.5 pri-Amyl 52. lg. None H=2(i. lg. 55.4 73.0 pri-Amyl 511g. PdCL-lg. B=26.lg. 92.6 91.5 pri-Amyl 52. lg. None A=2 1 .fig. [L8 9| .5pri-Amyl 52.lg. PdCL -lg. A=2 l .(ig. 78.9 95.0

alcohol is only impurity The product of the process of the presentinvention exhibits superior properties as a flotation reagent. as setforth in the following additional examples.

EXAMPLES lV-Vlll In the following examples. comminuted refractorysulfide ores were subjected to separate froth flotation operations inthe presence of the reagents indicated. but. otherwise were treatedunder substantially identical conditions. with the production ofconcentrate and tailing products of the analysis indicated.

The standard reagent referred to was a commercial isopropyl ethylthionocarbamate. accepted at the time as being effective in treating theores tested. but apparently containing 3 to 6% impurities.

IV Test No. l. 2. 3. 4.

Orc:PiCu l.2l5 l2l5 lllfi I.Zl5 Concentrates: 4" (u i198 Ill} I500 I5 05Tails. '4 (u .245 .226 4l9 365 4 Recovery Rt 40 82.92 hT-tl 71 (i9Reagents. Pounds Per Ton Standard Reagent .00 04 7 lsopropyl l-lthylThtonocarhamate .06 04 In this test. at the higher addition level. theuse of the product of the invention caused an increase in copperrecovery of L527: with a corresponding decrease in copper values lost astails. At the lower addition level. use of the product of the inventionwas even more impressive. increasing copper recovery by 4.28%.

In this test. with a less-rich ore. improvement at a low level ofaddition amounted to H871.

VI Test No. I. 2.

Ore: Cu L020 L020 Concentrates: 1 Cu 8.48 9.22 Tails: '/r (.u .236 .2l4'/1 Recovery 79.02 R088 Reagents. Pounds Per Ton Standard Reagent .04lsopropyl Ethyl Thionoearhamate .04

VII Test No. l. 2.

Ore: '4 Cu .869 .869 Concentrates: '4 (u l2.l4 H93 Tails: '4 Cu .176.154 '14 Recovery 80.3] 83.3!

Reagents. Pounds Per Ton Standard Reagent .04 lsopropyl EthylThionocarbamatc .04

VIII Test No. l. 2. 3.

Ore: '4 (u .897 .897 .897 Concentrates: '1 Cu 9.70 10.40 9.93 Tails: 4(.u .20! .lli) J89 '& Recovery 79.26 803K 8049 Reagents. Pounds Per TonStandard Reagent .04 lsohutyl l-ithyl 'lhtonocarhatnate .04'l'hionoearhanmte .04

In tests Vl-Vlll. with widely varying ores. the improvement broughtabout by use ol'the product of the invention was. respectively. 1.869%.2.4l'71 and l.23 r. In the latter instance. it should be noted. thatisobutyl esters (ethyl and methyl) were used rather than the isopropylethyl ester used in the other examples. Other tests have shown that theisopropyl ester is indeed to be preferred for some ores. The length ofthe carbon chain on the other alkyl group is not considered significantand is nominally limited to [-6.

In the foregoing tests it is considered that the differences in puritybetween the standard reagent (3-6 2) and the product of the invention(less than 2% l are too small to account for the improved resultsobtained. It is felt. therefore. that some unknown factor associatedwith the process of the invention must be responsible for theimprovement.

Various changes in the details. steps. materials and arrangements ofparts. which have been herein described and illustrated in order toexplain the nature of the invention. may be made by those skilled in theart within the principle and scope of the invention as defined in theappended claims.

What is claimed is:

I. In a process for the production of dialkyl thionocarbamates byreaction of an alkyl amine containing l to 6 carbon atoms with a loweralkyl. alkali metal xanthate. the improvement comprising carrying outsaid reaction in the presence of palladium ions.

2. The process as claimed in claim I, wherein said reaction is carriedout at a temperature in the range of to 90 C. for from V2 to l8 hours.

3. In a proces for the production ofan alkyl-isopropyl thionocarbamateby reaction of an alkyl amine containing 1 to 6 carbon atoms with analkali metal isopropyl xanthate. the improvement comprising carrying outsaid reaction in the presence of a dissolved catalyst selected from thegroup consisting of palladium and nickel ions.

4. The process as claimed in claim 3. wherein said catalyst is nickel.and said reaction is carried out at a temperature in the range of to C.for from 4 to 18 hours.

5. The process as claimed in claim 3, wherein said catalyst ispalladium. and said reaction is carried out at a temperature in therange of 50 to 90 C. for from to l8 hours.

6. A process for the production of dialkyl thionocarbamates comprising:

reacting a stoichiometric excess of an alkyl amine having from I to 6carbon atoms with an aqueous solution of a lower alkyl. alkali metalxanthate at a temperature in the range of 50 to 90C. for from /5 to 18hours in the presence of palladium ions; and

separating the resulting organic and aqueous phases and recovering saidthionocarbamate from said organic phase.

7. The process as claimed in claim 6, wherein said excess is in therange of about 20 to l007z.

8. The process as claimed in claim 6, wherein the amount of saidpalladium present is at least 0.002 mols per mol of xanthate.

9. The process as claimed in claim 6, wherein said xanthate solution isa technical grade xanthate containing dissolved carbon disulfide and nomore than 2 percent free alkali.

10. A process for the production of an alkyl isopropyl thionocarbamatecomprising:

reacting a stoichiometric excess of an alkyl amine having from I to 6carbon atoms with an aqueous solution of an alkali metal isopropylxanthate at a temperature in the range of 60 to 90 C. for from 4 to [8hours in the presence of nickel ions; and

separating the resulting organic and aqueous phases and recovering saidthionocarbamate from said organic phase.

13. The process as claimed in claim ll). wherein said xanthate mlutiunis a technical xanthate containing dissolved carbon disulfide and nomore than 1 percent free alkali.

1. IN A PROCESS FOR THE PRODUCTION OF DIALKYL THIONOCARBAMATES BYREACTION OF AN ALKYL AMINE CONTAINING 1 TO 6 CARBON ATOMS WITH A LOWERALKYL, ALKLI METAL XANTHATE, THE IMPROVEMENT COMPRISING CARRYING OUTSAID REACTION IN THE PRESENCE OF PALLADIUM IONS.
 2. The process asclaimed in claim 1, wherein said reaction is carried out at atemperature in the range of 50* to 90* C. for from 1/2 to 18 hours. 3.In a proces for the production of an alkyl-isopropyl thionocarbamate byreaction of an alkyl amine containing 1 to 6 carbon atoms with an alkalimetal isopropyl xanthate, the improvement comprising carrying out saidreaction in the presence of a dissolved catalyst selected from the groupconsisting of palladium and nickel ions.
 4. The process as claimed inclaim 3, wherein said catalyst is nickel, and said reaction is carriedout at a temperature in the range of 60* to 90* C. for from 4 to 18hours.
 5. The process as claimed in claim 3, wherein said catalyst ispalladium, and said reaction is carried out at a temperature in therange of 50* to 90* C. for from 1/2 to 18 hours.
 6. A process for theproduction of dialkyl thionocarbamates comprising: reacting astoichiometric excess of an alkyl amine having from 1 to 6 carbon atomswith an aqueous solution of a lower alkyl, alkali metal xanthate at atemperature in the range of 50* to 90*C. for from 1/2 to 18 hours in thepresence of palladium ions; and separating the resulting organic andaqueous phases and recovering said thionocarbamate from said organicphase.
 7. The process as claimed in claim 6, wherein said excess is inthe range of about 20 to 100%.
 8. The process as claimed in claim 6,wherein the amount of said palladium present is at least 0.002 mols permol of xanthate.
 9. The process as claimed in claim 6, wherein saidxanthate solution is a technical grade xanthate containing dissolvedcarbon disulfide and no more than 2 percent free alkali.
 10. A processfor the production of an alkyl-isopropyl thionocarbamate comprising:reacting a stoichiometric excess of an alkyl amine having from 1 to 6carbon atoms with an aqueous solution of an alkali metal isopropylxanthate at a temperature in the range of 60* to 90* C. for from 4 to 18hours in the presence of nickel ions; and separating the resultingorganic and aqueous phases and recovering said thionocarbamate from saidorganic phase.
 11. The process as claimed in claim 10, wherein saidexcess is in the range of 20 to 100%.
 12. The process as claimed inclaim 10, wherein the amount of said nickel present is at least 0.01mols per mol of xanthate.
 13. The process as claimed in claim 10,wherein said xanthate solution is a technical xanthate containingdissolved carbon disulfide and no more than 1 percent free alkali.